The thrust reverser of a turbojet is a system that makes it possible to deviate in the opposite direction a portion of the flow flowing in the turbojet, in order to brake the aircraft equipped with this turbojet. This deviation is obtained by the interposition of obstacles in the stream of the flow, these obstacles being displaced from a folded position to a deployed position by actuating means. For example, thrust reversers are known of the type with grids, doors, and clamshells.
In prior art, the means for actuating of a thrust reverser include one or several hydraulic actuators which are supplied with pressurized fluid by at least one hydraulic circuit of the aircraft which also supplies means for actuating components of the aircraft such as spoilers, air brakes, etc., used for the flight controls of this aircraft. The fluid pressure at the exit of this type of hydraulic circuit is relative substantial (for example of a magnitude of 200 bars), which makes it possible to use a relatively compact cylinder to manoeuvre the obstacles of the thrust reverser.
However, this technology has many disadvantages.
In the event of a failure of the hydraulic pump of the circuit, the thrust reverser can no longer be actuated. It may be necessary to provide a hydraulic accumulator in the nacelle of the turbomachine, this accumulator making it possible to store pressurised fluid and top release this fluid on demand in order to use the thrust reverser in the event of a pump breakdown.
In addition, the hydraulic fluid used (Skydrol® in general) is sensitive to the variations in temperature. When the surrounding temperature is low (minimum operating temperature less than −15° C.), the hydraulic fluid has substantial viscosity, which increases the time required to manoeuvre the thrust reverser for its deployment and its folding back. On the contrary, when the surrounding temperature is high (maximum operating temperature greater than 90° C.), the hydraulic fluid becomes acidic and high aggressive to certain materials, which can result in leaks and pollutions of the turbojet. In the event of a leak of this fluid, it is then no longer possible to control the thrust reverser and the components of the flight controls of the aircraft which are actuated by means of the same hydraulic circuit. This hydraulic fluid is moreover flammable and it is preferable to provide a fire stop device of the supply of the thrust reverser in order to prevent an engine fire in the event of a leak of this fluid.
The deployment or the folding back of the thrust reverser must be rapid (it lasts less than two seconds) and in general takes place during the landing of the aircraft at a moment when the components of the flight controls such as the spoilers and the air brakes as well as the landing gear are also actuated. The hydraulic circuit of the aircraft must be dimensioned to deliver a high enough flow of pressurised fluid to each of these elements, which results in a more involved hydraulic installation.
Means for actuating of a thrust reverser with an electric engine, or with pneumatic cylinder could be proposed but these technologies cannot be used for small engines, due to their mass and their cost.